This invention relates to engines that employ pistons, and more particularly, relates to engines employing rotating liquid as a piston.
Engines employing pistons are well known in the prior art. In general, these prior art engines employ a piston which moves up and down inside a cylinder with the piston connected to a crankshaft via a connecting rod and the crankshaft then translates the linear up and down motion into rotational motion. This rotational motion is then used, via a gear box or other transmission mechanisms, to cause rotation of a drive mechanism to thereby impart motion to a movable vehicle. For example, the rotational motion from the crankshaft may be used to drive an electric generator, wheels, a propeller on an airplane, or a propeller for a boat. In general, such piston engines are used to transform the thermal energy from the combustion of a hydrocarbon fuel into kinetic energy associated with work, such as the movement of a vehicle.
However, conventional piston engines have relatively complicated designs and have large energy losses associated with the conversion of the energy from the combustion of the fuel into the kinetic energy associated with work or movement. In addition, these engines require complicated cooling systems to remove the heat of combustion (for internal combustion engines), and lubricating devices to provide a continuous flow of lubricating fluids to metallic parts that are rotationally or slidingly contacting each other. Further, these engines are generally very heavy because of all the associated auxiliary equipment necessary to support the engine and to convert the rotational energy into an appropriate and different form of easily useable energy. Such engines employing pistons may be internal combustion engines (otto and/or diesel cycles) or external combustion engines (such as a steam engine).
A flat, liquid piston external combustion engine is known in the prior art (Liquid Piston Stirling Engines, by C. D. West, Van Nostarand Reinhold Company, 1983, p. 5, FIG. 1.5) and is depicted in FIG. 1. This liquid piston engine is very simple in its design and does not employ complicated mechanical parts (such as pistons, connecting rods, and crankshafts) or any other type of transmission element. The engine basically consists of two cylindrical vessels that are partially filled with liquid and are interconnected by two parallel conduits or pipes, with the conduits or pipes having appropriate valves where the conduit or pipe connects with the cylindrical vessel. The valves ensure that flow through a conduit or pipe is only in one direction. When the air above the fluid in one of the cylinders is heated, via heat from an external combustion source, the pressure of the air expansion (from heat) forces the liquid to move from the "heated" first cylinder into the "cool" second cylinder through one of the one-way pipes interconnecting the two chambers. As the liquid flows from one cylinder to the other cylinder, it may then be used to rotate a hydromotor and the hydromotor may then perform useful work. This may continue until the expansion has reached some maximum amount, then the air in the first cylinder is "cooled" and the air in the second chamber is heated to drive the liquid in the opposite direction through the second one-way interconnecting pipe, and again via the hydromotor extract some work from the fluid flow.
The main drawback of an engine having a flat liquid piston is the poor stability of its top surface, because this surface is liquid. More particularly, when the "piston" is near its top dead center, its speed becomes zero but the acceleration normal to the top surface is maximum, and if this acceleration exceeds the acceleration of the force of gravity then the flat liquid surface of the piston is destroyed by this acceleration. Under these conditions a stability criterion that is the ratio of gravity (g) divided by the acceleration (a) of the piston must be more than one so that no liquid will leave the surface of the flat liquid surface of the piston because of such acceleration inertia.
Such a flat liquid piston engine has only been run successfully under laboratory conditions. The power from one of these flat liquid piston machines is, at best, only several watts and their efficiency is not more than about one percent. Further, the frequency of this engine, i.e, the frequency of the shifting of the fluid back and forth between the two cylinders, is only a fraction of a Hz in order to avoid the instability of the top surface of the liquid piston. Additionally, this engine is very sensitive to orientation, vibrations and inertial overloading; any engine that is associated with movement of vehicles must be insensitive to these factors.
These and other limitations and disadvantages of the prior art are overcome by the present invention, however, and improved methods and apparatus are provided for an engine employing rotating liquid as a piston.